This invention relates generally to waste effluent treatment systems and processes and more particularly to a waste effluent treatment system and process for agricultural animal waste.
Over the past decades, there has been a shift from smaller localized family farms toward larger integrated confinement agricultural operations. Specifically, large agricultural operations may utilize confinement barns to house a large number of livestock such as swine, poultry or dairy cows. The dairy industry operates using large farms that house thousands of animals in a relatively small land area. While these larger agricultural operations have numerous advantages, attendant with these larger facilities are potential pollution problems relating to the handling and treatment of manure and wastewater. By way of example, pollution problems associated with liquid animal waste include nitrogen, phosphorus, solids, bacteria and foul odors that result from anaerobic storage of liquid manures. Environmental concerns more specifically center on odor and water quality issues.
It is well known that the storage and treatment of manure and management of manure in confined animal feeding operations, such as those used for dairy, poultry and swine, is one of the most difficult, expensive and potentially limiting problems facing the agricultural industry today. Animal excrement, in the form of manure, contains high amounts of nitrogen, phosphorous and other chemical constituents such as salts, which derives from the undigested portion of animal feed, that make such manure undesirable for contact with fresh water sources, such as rivers and underground aquifers, and difficult to treat or remove once it contaminates fresh water. As a result, manure management is an important task for every confined animal feeding operation and can require a significant amount of resources, including labor, land, equipment and financial resources.
Farmers often create storage lagoons or basins on their farms to accumulate and store the flushed wastewater, feces and urine until an appropriate time to distribute the wastes over the land. The wastewater can be utilized as flush water not only to reduce the amount of water consumed by the animal production, but also to conserve the capacity of the lagoon. Using the lagoon water for flushing reduces the water consumption by 70-90% and proportionally reduces the required size of the lagoon. The wastewater is usually stored until crop harvest and applied to cropland in place of a commercial fertilizer prior to the next crop.
Typically, during the storage process, due to the large volume of animal waste entering the lagoon, there is insufficient oxygen present to support the growth of aerobic cultures and/or aerobic biological activity. In the absence of the desired oxygen and highly concentrated manure constituents, the microbial growth in the lagoon converts to anaerobic activity. This anaerobic activity leads to what is commonly known as a “septic” lagoon. In a septic lagoon, a very foul odor is present from the production of hydrogen sulfide, organic-sulfide compounds, organic acids, etc. When the accumulated waste liquid is distributed over the cropland by spray irrigation, the foul smelling volatile gases are liberated, producing a very undesirable environment.
Aeration equipment can be installed to provide sufficient dissolved oxygen to maintain an aerobic culture. However, the energy cost and mechanical maintenance expenses as well as equipment costs to operate the aerobic treatment can be cost prohibitive. There are several methods of aeration available. Surface aerators are commonly used in large open areas. The surface aerator consists of an electric motor driven impeller suspended in the throat of a venturi with the entire unit mounted on a float to suspend the impeller just below the surface. As the impeller spins, it pumps the water up forming a large circular spray. Oxygen is dissolved in the water as it falls through the air. The amount of water spray and subsequently the amount of oxygen dissolved is directly proportioned to the amount of water pumped and therefore the horsepower of the motor and energy consumed.
The foul odors of wastewater become apparent in most operations, including, but not limited to:                (1) When the stored water is returned to the barns as flush water, odors are liberated;        (2) Spray operations: when the wastewater is applied to the cropland by spray irrigation (most common method), the liquid is pumped under high pressure through a nozzle and sprayed over large area. The spray area as well as all areas downwind has a putrid odor and is very undesirable; and        (3) Winter thermal changeover: In the winter to spring of the year, the normal thermocline of the lagoon is disturbed. Due to the temperature differences, the bottom layers roll to the surface, creating an extra heavy liberation of noxious odors. Another disadvantage of the temperature change and decreased temperature in the lagoon causes a decrease in the metabolic rate of the bacteria which are using the organic portion of the stored manure as food nutrients as energy.        
Over the past few decades, more people have found it desirable to live in a country atmosphere rather than the conventional city life, resulting in a greater number of people living near agricultural centers. The foul odor coming from the storage basins and lagoons and spray fields has increasingly become a major environmental issue. For example, in 1997, the state of North Carolina passed a moratorium prohibiting the creation of any new anaerobic lagoons. New rules are being considered to phase out the use of all anaerobic lagoons because of the environmental and social problems.
A conventional prior art waste treatment system is shown in FIG. 1. The treatment system includes a confinement structure or barn 112, having waste slurry pits 114. Fresh water is piped in through fresh water inlet 116, mixes with recycled lagoon water or recycled manure wastewater 134 and washes through the barn 112 to slurry pits 114. The result is a waste slurry, typically having 2-3% total solids. The waste slurry is then directed through piping 118 into a lagoon 120.
A typical 8000 head grow/finish swine farm requires a 2-5 acre lagoon, dependent on regional climate, use or disposal of treated waste, seasonal storage requirements, and demands of regulatory permits. Water is then removed from lagoon 120 by pump 126 to be recycled by piping 128, 134 back to the barn 112 through inlet 136 for further waste removal. Additionally, the diluted slurry may be diverted through piping 130 for land application 132.
The foregoing illustrates limitations known to exist in present agricultural animal waste treatment systems. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.